1. Field of the Invention
This invention relates in general to packaged electronic devices and specifically to lead frames for packaged electronic devices.
2. Description of the Related Art
Electrical circuits such as integrated circuits can be implemented in packaged electronic devices. A packaged electronic device may include one or more lead frames and one or more die for implementing electrical circuits of the packaged electronic device. In some embodiments, the die and lead frame(s) may be encapsulated with an encapsulant.
Because the packaging of die includes different materials (e.g. metal, encapsulant), temperature variations may cause the packaged die to be stressed during manufacture and operating conditions due to the differences in thermal expansion and other material properties of the different materials. For some packaged electronic devices that include some types of circuits and transducers (e.g. a sensor), this stress may affect the operation of the device.
FIG. 1 is a partial cross sectional view of a prior art packaged electronic device. Packaged electronic device 101 includes a first die 105 and a second die 107 attached to the top of die 105. Die 105 and die 107 are utilized to implement a sensor. Located between die 105 and lead frame 103 are four rubber or adhesive pads (with rubber or adhesive pads 113 and 111 being shown in FIG. 1). The rubber pads isolate die 105 from stress along lead frame 103. The rubber or adhesive pads are attached to a flag structure of lead frame 103. Prior to encapsulation, die 105, die 107 and the rubber pads are enclosed in a gel 109 for further stress isolation. This stress isolation may be done for the sensor to function electrically within accepted specifications in the operating temperature range. After wire bonding, the entire assembly is encapsulated with encapsulant 115 at an elevated temperature. After cooling back to room temperature, an air gap (not shown) is formed between the gel and encapsulant due to a much faster shrinkage of the gel compared to the encapsulant. The air gap shields die 105 and die 107 from the packaging stress caused by encapsulant 115 and lead frame 103.
Such a stress isolation process is complicated and the process control is often difficult. In addition, to accommodate the inclusion of the gel, the resulting package that is simpler, smaller, and with significantly reduced packaging stress to an electronic device.
The use of the same reference symbols in different drawings indicates identical items unless otherwise noted.